1. Field of the Invention
The present invention relates to a test method using a plurality of oscillation circuits. The invention also relates to an element substrate for carrying out the test method, and a manufacturing method for a semiconductor device using the test method.
2. Description of the Related Art
In a manufacturing process of a semiconductor device such as a display device, which includes a plurality of steps such as etching and doping, an oscillation circuit as an evaluation circuit (hereinafter referred to as an oscillation circuit for evaluation) is provided over the same substrate as the semiconductor device such as a display device in order to evaluate electrical characteristics of a manufactured semiconductor element.
In conventional technologies, the oscillation frequency of a plurality of oscillation circuits for evaluation is measured by applying a needle called a probe to each of the oscillation circuits for evaluation. Such a measurement method using a probe is called a contact measurement method.
As a semiconductor device capable of using such a contact evaluation method, there are display devices such as a liquid crystal display device and an EL (Electro Luminescence) display device, as well as logic circuit devices such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), and a memory, and an RFID (Radio Frequency Identification) circuit device for communicating information wirelessly.
The oscillation circuit for evaluation includes a ring oscillator and a PLL (Phase Lock Loop). In addition, the oscillation circuit for evaluation generally includes a VCO (Voltage Control Oscillator) that is a component of the PLL, and an LC oscillation circuit having a coil and a capacitor.
In particular, the ring oscillator is generally often used for measurement of the electrical characteristics of a manufactured semiconductor element and evaluation of variations in electrical characteristics.
In the conventional measurement of oscillation circuits for evaluation, a probe is applied to a measuring terminal of each of the oscillation circuits for evaluation; therefore, it takes time to measure including movement of the probe.
In addition, a plurality of oscillation circuits for evaluation cannot be simultaneously measured in the conventional measurement of oscillation circuits. Accordingly, there is fear that a measurement environment such as parasitic capacitance, power supply, and temperature may change.
Since a plurality of oscillation circuits for measurement are not measured at the same time in the conventional measurement of oscillation circuits, measurement errors may differ for each measurement. The measurement errors are caused by errors of a measuring instrument or errors in reading.